My invention relates to an electrical measuring apparatus and process, and particularly to such an apparatus and process for measuring the resonant frequency and coefficient of coupling of a plurality of coupled piezoelectric resonators.
Piezoelectric resonators have reached a stage of development where they are used extensively in radio and electronic applications. A typical application uses a plurality of such resonators formed by two or more pairs of electrodes positioned on a single plate of piezoelectric material. This arrangement is sometimes called monolithic crystal. The mass loading of each pair of electrodes forming a resonator determines in part the resonant frequency of that resonator. Coupling between adjacent resonators is determined in part by the effective separation between adjacent resonators. By positioning a coupling strip between adjacent resonators, their effective separation is reduced and coupling is increased. In the manufacture of such a device, electrode material is deposited on the resonators such that their resonant frequencies are slightly lower than desired. The frequency of each resonator is increased to the desired value by removal of effective electrode mass from each pair of electrodes. Also the coupling strip between resonators is designed such that the effective separation between resonators is smaller than needed, yet such that if the coupling strip were completely removed the effective separation between resonators would produce an effective coupling which would be too small. The coupling strips are reduced in size, thereby increasing the effective spacing between resonators, to decrease the coupling between adjacent resonators to the desired value. Where relatively large quantities of such devices are manufactured, automated techniques using laser trimming apparatus are used to advantage. Such automated techniques need or require an apparatus and a process for measuring the resonant frequency and the coefficient of coupling of a plurality of coupled piezoelectric resonators in order that the resonators can be easily and quickly trimmed to the desired values.
Accordingly, a primary object of my invention is to provide a new and improved apparatus for measuring the resonant frequency and coefficient of coupling of a plurality of coupled piezoelectric resonators.
Another object of my invention is to provide a new and improved process for measuring the resonant frequency and coefficient of coupling of a plurality of coupled piezoelectric resonators.
Another and fairly specific object of my invention is to provide novel apparatus that lends itself to measuring the resonant frequency and coefficient of coupling of a plurality of coupled piezoelectric resonators for use with automated trimming applications.